Field of the Invention
The present invention relates to an improved process for preparing derivatives of isobutene copolymers. The present invention further relates to novel isobutene copolymer derivatives.
Description of the Related Art Including Information Disclosed Under 37 C.F.R. §§1.97 and 1.98
Isobutene copolymer derivatives are frequently obtained from so-called high-reactivity polyisobutenes. In contrast to so-called low-reactivity polyisobutenes, high-reactivity polyisobutenes are understood to mean those polyisobutenes which comprise a high content of terminal ethylenic double bonds (α-double bonds), specifically in practice of 80 mol % or more, based on the individual chain ends of the polyisobutene macromolecules. Typically, vinylidene groups are understood to mean those double bonds whose position in the polyisobutene macromolecule is described by the general formula
i.e. the double bond is present in an α position in the polymer chain. “Polymer” represents the polyisobutene radical shortened by one isobutene unit. The vinylidene groups exhibit the highest reactivity, for example in the thermal addition onto sterically demanding reactants such as maleic anhydride, whereas a double bond further toward the interior of the macromolecules in most cases exhibits lower reactivity, if any, in functionalization reactions.
The uses of such high-reactivity polyisobutenes include use as intermediates for preparing additives for lubricants and fuels; for example, according to the teaching of DE-A 27 02 604, they are reacted with maleic anhydride to give polyisobutenylsuccinic anhydrides. However, the high-reactivity polyisobutenes obtainable by the process of DE-A 27 02 604 by cationic polymerization of isobutene in the liquid phase in the presence of boron trifluoride as a catalyst have some disadvantages: for example they have a relatively high polydispersity. The polydispersity is a measure of the molecular weight distribution of the resulting polymer chains and corresponds to the quotient of weight-average molecular weight Mw and number-average molecular weight Mn (PDI=Mw/Mn).
Polyisobutenes with a similarly high proportion of terminal double bonds but with a narrower molecular weight distribution are, for example, obtainable by the process of EP-A 145 235, U.S. Pat. No. 5,408,018 and WO 99/64482, the polymerization being effected in the presence of a deactivated catalyst, for example of a complex of boron trifluoride with alcohols and/or ethers.
High-reactivity polyisobutenes are also obtainable by living cationic polymerization of isobutene and subsequent dehydrohalogenation of the resulting polymerization product, for example by the process from U.S. Pat. No. 5,340,881. However, such a process is complex since the halogen end group introduced with the living cationic polymerization has to be eliminated in a separate step in order to generate the double bond.
It has additionally been known for some time that the Lewis acid aluminum trichloride can also be used as a polymerization catalyst for isobutene, for example from High Polymers, volume XXIV (part 2), p. 713-733 (editor: Edward C. Leonard), J. Wiley & Sons publishers, New York, 1971.
The European patent application with the reference number 10157068.7, which was yet to be published at the priority date of the present application, describes a process for preparing high-reactivity isobutene homo- or copolymers by polymerization in the presence of an aluminum trihalide-donor complex with is effective as a polymerization catalyst or of an alkyl aluminum halide-donor complex which comprises, as the donor, an organic compound with at least one ether function or a carboxylic ester function, and optionally an organic hydroxyl compound, an organic halogen compound or water as an initiator. Further reactions with the high-reactivity isobutene homo- or copolymers thus prepared are not described therein.
CN 101955558 A discloses that iron(III) chloride is suitable as a coinitiator in the cationic isobutene polymerization for preparation of high-reactivity polyisobutenes and copolymers thereof. The initiators recommended are water, phenols, protic acids such as sulfuric acid, tertiary alcohols, tertiary chlorides, tertiary carboxylic esters and carboxylic acids themselves. The complexing agents mentioned for the systems which initiate the polymerization are especially alkyl ethers.
WO 95/07944 describes copolymers which bear functional groups and are obtainable by free-radical copolymerization of (a) 20 to 60 mol % of at least one monoethenic unsaturated C4- to C6-dicarboxylic acid or anhydride thereof, (b) 10 to 70 mol % of at least one oligomer of propene or of a branched 1-olefin having 4 to 10 carbon atoms, such as isobutene, and a mean molecular weight Mw of 300 to 5000, and (c) 1 to 50 mol % of at least one monoethylenically unsaturated compound which is copolymerizable with monomers (a) and (b), and subsequent functionalization of the copolymer via the anhydride or carboxyl groups with amines. These copolymers are suitable as lubricant and fuel additives.
The preparation methods known from the prior art for derivatives of copolymers based on high-reactivity polyisobutenes, however, have a series of deficiencies. For instance, the content of terminal vinylidene double bonds in the precursor is still too low. The yields in the conversion to the derivatives are in need of improvement. The appearance and the consistency of the derivatives, especially the suppression of discoloration, for example caused by undesired carbonization reactions in the course of thermal stress during derivatization, are still not optimal. Moreover, the physical properties of the derivatives, especially the viscosity behavior at low temperatures, as can occur, for example, in practical use in lubricant oils, and the solubility, especially in polar media, the thermal stability and the storage stability of the derivatives are still in need of improvement. The derivatization processes known from the prior art for isobutene copolymers which proceed from isobutene polymers prepared by means of fluorinated polymerization catalysts have the disadvantage that they trigger corrosion on numerous metallic materials and steel types owing to the residual fluorine content.